Dave,
I agree she won't likely spend any time behind bars. I also agree this is premature as there's not been a trial as yet, much less a conviction.
There is one point, however, on which I disagree. You said you believed this could be slanderous. It could not. I think you may have meant libelous. Slander is spoken while libel is written. /w3tcompact/icons/smile.gif
It could be considered to be libelous were Stewart to sue and be able to prove quantifiable damages as a direct, sole and exclusive result of this.
Frankly, I think Ms. Stewart is taking most of these attempts at humor at her expense pretty well in stride. While shopping recently she was seen to pick up a shirt with a parody of her on the front, read it, smile and put it back on the rack.